Protective and decorative sheet material having a transparent topcoat

ABSTRACT

A protective and decorative sheet material for covering substrates comprises 
     a flexible carrier film, 
     a paint layer adhered to one surface of the carrier film containing light reflective flakes; 
     a transparent polymeric topcoat overlying and adhered to the paint layer having a thickness of at least about 0.1 millimeter. 
     The sheet material has a substantially unstressed relaxed state and a relaxed area and is heat softenable to a substantially plastic state in which it is extendable to an extended state having an extended area up to at least 50% greater than the relaxed area. The paint and topcoat layers have substantially uniform quality and appearance in both the relaxed and extended states. The thick transparent topcoat provides improved retention of gloss and distinctness of image when the sheet material is stretched. A method of preparing the sheet material comprises the step of extruding in laminar flow a layer of a crosslinkable transparent topcoat composition over the paint layer.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 116,426 filed Nov. 3, 1987 in the name of G. G. Reafler nowabandoned.

FIELD OF THE INVENTION

This invention relates to a protective and decorative sheet material andto a method for the preparation thereof. More specifically, it relatesto a flexible, thermoformable sheet material that can be bonded tovarious substrates, including exterior automotive panels, as aprotective and decorative covering.

BACKGROUND OF THE INVENTION

The invention will be described with reference to providing protectiveand decorative finishes on exterior automotive panels, but it should beunderstood that the automobile is only one of many substrates to whichthe sheet material of the invention can be applied.

As pointed out in an article by Alan J. Backhouse entitled "Routes ToLow Pollution Glamour Metallic Automotive Finishes", Journal of CoatingsTechnology, Vol. 54, No. 693, pages 83-90, October 1982, there is agrowing need to reduce the amount of atmospheric pollution caused bysolvents emitted during industrial painting processes. Many differentapproaches have been proposed. For example, efforts have been made toreplace the solvent-based paints used for automobiles with water-basedpaints. Work has also been done on the use of high solids formulationsto lessen the emission or organic solvents. However, the application ofautomotive finishes is a highly demanding art because of the extremelyhigh quality of the surface finish required and because of the commonapplication of metallic finishes to provide what Backhouse refers to as"high stylistic effects". Accordingly, past efforts to replace the lowviscosity, low-solids-content paint formulations conventionally used inspray painting operations in the automotive industry have met withlimited success.

A more promising approach is to eliminate entirely the need for spraypainting. Elimination of spray painting, or reduction in its use, wouldnot only reduce atmospheric pollution, but would provide cost savings inthat spray painting operations are so wasteful that more than half ofthe paint may be wasted. A means for achieving such goal exists throughthe use of a pre-formed thermoplastic sheet material which can be bondedto the panel to provide the protective and decorative coating. Suchtechniques have been utilized for interior automobile panels asdescribed, for example, in U.S. Pat. No. 3,551,232 issued Dec. 29, 1970.

The objective of U.S. Pat. No. 3,551,232 is to overcome the problems ofbubbling and blistering of the resin sheet that tend to occur in thevacuum-forming process. It achieves this by use of an adhesivecontaining an inert particulate filler which minimizes the entrapment ofair.

To employ a process of the type described in U.S. Pat. No. 3,511,232with exterior automotive panels presents a greater challenge. Thesurface appearance of such panels is of critical importance, so that itis necessary not only to avoid bubbling or blistering caused byentrapped air, but to provide a protective and decorative coating thatwill equal or exceed the quality of a spray-painted surface.Furthermore, exterior automotive panels present a particular problem inview of the difficulty of smoothly adhering a flexible sheet material toa curved substrate and the difficulty of doing so while maintaining overthe entire surface a uniform color intensity.

Efforts have been made by others to produce a flexible and stretchablesheet material having these capabilities through the application of oneor more paint layers to the surface of a thermoformable polymericsupport. However, prior to the invention of Reafler, U.S. patentapplication Ser. No. 116,426 now abandoned, it is believed that theseefforts have resulted in products having numerous coating defects and inwhich the paint layer does not have the high degree of uniformity whichpermits the sheet material to undergo the stresses of thermoforming andyet meet the exacting standards of an exterior automotive finish.

In accordance with the invention of the Reafler patent application, aflexible and stretchable sheet material that is (1) capable of meetingthe requirements of an exterior automotive finish and (2) capable ofwithstanding the stretching and bending forces involved in bonding it toexterior automotive panels is produced by precision coating techniqueswhich provide exacting control of the thickness and thickness uniformityof the coatings. Moreover, such coating techniques provide essentiallydefect-free coatings having a substantially uniform quality andappearance.

The sheet material of the Reafler application comprises a thin flexiblecarrier film, and a protective and decorative paint layer, also known asa basecoat, adhered to one surface of the carrier film. The carrier filmhas heat-softening and tensile elongation properties which adapt it touse in the thermoforming process and the paint layer has compatible heatsoftening and tensile elongation properties. As a result, the sheetmaterial can undergo substantial elongation without crazing ordelamination of the protective and decorative paint layer.

The sheet material has a substantially unstressed relaxed state and arelaxed area and is heat softenable to a substantially plastic state inwhich it is plastically extendable and formable over irregular surfacesto an extended state having an extended area at least 50% greater thanthe relaxed area. The protective and decorative paint layer has asubstantially uniform quality and appearance both in the relaxed andextended states. The sheet material can be stretched and bonded to athree-dimensional substrate as a smooth and wrinkle-free protective anddecorative coating of uniformly attractive appearance.

The Reafler application also discloses a process for the manufacture ofthe sheet material comprising the steps of: providing a thin, flexiblecarrier film; providing a fluid protective and decorative film-formingcomposition; forming a laminar flow of the composition and directing theflow into contact with the surface of the carrier film to form thereon aprotective and decorative layer of substantially uniform thickness; andconverting the protective and decorative layer to a dry and tack-freestate. The protective and decorative film-forming composition isadvantageously coated over an adhesion-promoting tie-layer. The processprovides an essentially defect-free coating with a high degree ofuniformity of layer thickness and a substantially uniform quality andappearance.

In an important embodiment of the sheet material, for which the presentinvention provides an improvement, the paint layer comprises afilm-forming binder, a colorant and generally flat, light-reflectingparticles which are oriented by the laminar flow process; that is, theyare preferentially oriented substantially parallel to the surface of thelayer. This provides a paint layer characterized by a high degree ofgeometric metamerism, a property commonly referred to as "flop."

The preferred embodiment of the sheet material, for which the presentinvention provides an improvement, also includes a transparent topcoatcomprising a clear or lightly colored polymer. This topcoat is alsocalled a clearcoat. The carrier film, paint layer and topcoat layer havecompatible heat-softening and tensile elongation properties which renderthe sheet material suitable for use in a thermoforming process. Also thecarrier film, paint layer and topcoat layers are of such uniformcharacter that the sheet material has substantially the same uniformityof appearance before and after the thermoforming process.

The transparent topcoat provides a number of desired properties. Theseinclude resistance to abrasion and to weathering. It can also improvethe surface qualities of gloss and distinctness of image (DOI). Sincethe sheet materials are especially intended for use as automotivecoverings which demand high gloss and other surface qualities; furtherimprovement in these qualities is desirable. Especially it is desirableto reduce or eliminate any tendency toward loss of gloss or of DOI whenthe material is stretched during thermoforming. Since the paint layerand clearcoat are coated on stretchable carrier films rather than onrigid surfaces and are coated by laminar flow methods rather than by theusual spraying processes for automotive finishes, the existingautomotive finishing literature gives little or no guidance as to waysfor improving or retaining the gloss or DOI of these sheet materialswhen stretched.

SUMMARY OF THE INVENTION

The present invention relates to the embodiment of the invention of theparent application wherein the sheet material has a transparent,polymeric topcoat and the paint layer contains light reflective flakes.It provides an improvement by reducing or eliminating loss of gloss andDOI of the sheet material when it is stretched.

Accordingly, the sheet material of the invention comprises

a thin flexible carrier film;

a protective and decorative paint layer adhered to one surface of thecarrier film; the paint layer having an outer surface and containinggenerally flat light reflective flakes; and

a transparent topcoat layer overlying the paint layer, the topcoat layerhaving a thickness of at least about 0.1 millimeter. The sheet materialhas a substantially unstressed relaxed state and a relaxed area and isheat softenable to a substantially plastic state in which it isplastically extendable and formable over irregular surfaces to anextended state having an extended area at least 50% greater than therelaxed area. The paint layer is adhered to the carrier film and thetopcoat layer is adhered to the paint layer. The sheet material has asubstantially uniform quality and appearance both in its relaxed and itsextended states.

The invention also includes the method by which the sheet material ofthe invention is manufactured. This method comprises continuouslypassing a carrier film web having a light reflective flake-containingpaint layer thereon in close proximity to the narrow extrusion slot ofan extrusion coating hopper and extruding in laminar flow over the paintlayer, a crosslinking, transparent topcoat composition,

passing the web having a wet topcoat layer directly from the coatinghopper to a drying chamber wherein the topcoat layer is dried and curedin a series of stages of successively increasing temperatures,

the speed of the web and the rate of extrusion of the topcoatcomposition being such that the thickness of the topcoat after drying isgreater than 0.1 mm, and

producing a dry topcoat layer of uniform thickness and appearance thatis substantially free of defects and that when stretched 50 percent hasa 20 degree gloss of at least 80.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are enlarged cross-sectional views of a sheet material ofthe present invention;

FIG. 3 is a diagrammatic side view of an apparatus for carrying out theprocess of the invention; and

FIG. 4 is a graphical representation of gloss measurements afterstretching of metallic and non-metallic paint-coated films havingclearcoats of different thicknesses.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1, there is shown a sheet material 10 inaccordance with the invention which comprises a flexible, thermoformablecarrier film 11, a thin tie-layer 12, and a paint layer 13 whichcontains light-reflective flakes such as aluminum flakes.

As a consequence of the laminar flow coating method by means of whichthe paint layer preferably is formed, the light reflective flakes arepreferentially oriented substantially parallel to the surface of thepaint layer. Most preferably, at least 75% of the flakes have anorientation within 12 degrees of parallelism with the paint layersurface. Over the paint layer is a thick layer 14 of a transparenttopcoat composition. This, preferably is a clear polymeric compositionand most preferably is crosslinked.

As shown in FIG. 2, on the opposite surface of carrier film 11 is coatedan optional adhesive layer 15. This can be, for example, apressure-sensitive or a heat-activated adhesive. An adhesive layer isdesirable when the sheet material is to be bonded to substrates such asautomobile parts by vacuum thermoforming. In other methods of bonding,such as the "in-mold" technique, which is a known method of laminating athermoplastic sheet to a plastic article while molding the article, anadhesive layer is not needed.

To protect the pressure-sensitive adhesive layer, a release sheet ofpolyester film 16 or the like can be adhered to it and then strippedaway before the sheet material is thermoformed and bonded to asubstrate. An optional release coating 17, e.g., a silicone coating, canbe on sheet 16 to aid in stripping it from the adhesive layer.

A characteristic of the described sheet material having a paint layerwhich contains light-reflective flakes such as aluminum flakes is thatit tends to lose gloss when stretched beyond certain limits duringthermoforming. This is true even when the sheet material has a glossy,clear, thin topcoat. In accordance with the present invention, the lossof gloss with stretching is reduced or eliminated if the transparenttopcoat is made sufficiently thick. More particularly, if the topcoat isat least 0.1 millimeter in thickness, marked improvement occurs in theretention of gloss by such sheet material when stretched.

Although the method of the present invention is characterizedparticularly by the manner in which the clearcoat is formed, other stepsof the overall method take place first. To describe the normal sequence,therefore, the earlier steps will be described first.

FIG. 3 illustrates diagrammatically a preferred coating and dryingapparatus which can be used in the method of the invention. Coatinghopper 31 is an extrusion coating hopper such as the type disclosed byBeguin, U.S. Pat. No. 2,681,294. The coating hopper extrudes in laminarflow through a narrow slot a horizontally extending bead of the coatingliquid in contact with the continuously moving film web 30. The coatingcomposition is thus coated as a uniform layer onto the surface of theweb. The first layer coated on the web can be tie-layer 12 or paintlayer 13, as shown in FIG. 1. In either case, the carrier film websupplied by roll 29, whether or not previously coated, passes in closeproximity to the narrow extrusion slot 31' of the coating hopper 31. Asthe web passes the hopper, a laminar flow of the coating composition isextruded on the web, the entire thickness of the coating for thatparticular pass being applied simultaneously across the width of theweb. Promptly after being coated, the web having the wet layer on itssurface is drawn through the drying apparatus.

The drying apparatus can be a flat bed and vertical loop, warm air dryergenerally of the type described in the aforementioned Reafler PatentApplication. It can also be modified for preferred conditions of dryingof aqueous paint layers as described in the copending patent applicationof Fronheiser et al, Ser. No. 166,083 filed Mar. 9, 1988, now U.S. Pat.No. 4,872,270.

The coated web 32 is pulled or drawn by take-up rollers not shown in thedrawing through successive stages of the drying apparatus. These includeinitial drying stages 33, 34, 35 and final curing stage 48. Preferablythe stages are at successively higher temperatures, the temperatures ofthe initial stages of the drying zone being mild. This is especiallydesirable when drying an aqueous paint which contains water and organicsolvents. The final stage or stages, however, can be at hightemperatures to remove residual liquids and/or to cure the crosslinkabletopcoat. For example, heated air can be introduced at 27° C., 43° C. and66° C. via lines 37 at stages 33, 34 and 35, respectively. Baffles 41divert the air flow away from the top of the film and cause it to flowto lower regions of the drying chamber. Sensing controls 45 and 46 aidin maintaining the appropriate air temperature and humidity by feedbackmechanisms not shown in the drawing. The speed of the web is such thatthe coating is subjected to elevated temperature for a substantial time,e.g., for 3 to 6 minutes, in the final stage 48 where the air isadmitted via line 40 at about 80° C.

Preferably, the moving web is also heated from its underside by contactwith metal rollers 36 and 43 and other rollers in the several dryingstages. These metal rollers of high conductivity are heated by the warmair and they transfer heat to the underside of the web, thus furtherincreasing its temperature. In the final stage 48, the web is heated toits highest temperature as it travels through a vertical path in afloating loop section, being guided by rollers 50 and air reversers ofthe plenums 49 to keep the coated side of the film out of contact withrollers 51. The dried film leaving stage 48 is wound on a take-up rollnot shown in the drawing.

In the preferred method of applying the thick transparent topcoat overthe paint layer, the paint layer is coated and dried and thereafter thetopcoat is applied by the same laminar flow coating method as describedabove for applying the tie-layer and paint layer. In this method, thefilm having on its surface the dried paint layer is again passed inclose proximity to the narrow extrusion slot of an extrusion coatinghopper 31, as shown in FIG. 3, from which the topcoat composition isextruded in laminar flow. Again, as with the paint layer, the entirethickness of topcoat to be applied in the particular pass is appliedsimultaneously across the width of the dried paint layer. Promptlythereafter the web having the wet topcoat layer on its surface is drawnthrough the drying apparatus.

The topcoat for the sheet material of the invention is extremely thick.It is normally preferred to coat such thick layers in two or more passesin order to dry them adequately. For example, if the topcoat drythickness is to be 0.12 mm, a first pass can coat and dry a layer of0.06 mm dry thickness and a second pass can coat and dry a second layerto raise the total dry thickness to 0.12 mm. For greater thickness,additional coating and drying passes can be carried out.

For optimum quality the stepwise increase in drying temperatures andother procedures such as humidity control, of the Fronheiser et al.drying process described in U.S. patent application Ser. No. 166,083,now U.S. Pat. No. 4,872,270, are also preferred for drying the topcoatlayer.

If the drying conditions are carefully controlled, e.g., by providingsmall temperature increases from stage to stage and having a lengthyresidence time in each stage, the entire thickness of the topcoat can becoated and dried in a single pass. However, since the topcoat isextremely thick in sheet materials of the invention, i.e., greater than0.1 mm when dry, the best quality is obtained when the topcoat is coatedand dried in two or more passes.

It is within the scope of the invention to coat the topcoatsimultaneously with the paint layer. This wet-on-wet method of coatingcan be carried out with laminar flow coating hoppers suitable forsimultaneous coating of multiple layers. Examples of such coatinghoppers include U.S. Pat. Nos. 2,761,419; 2,761,791 and 3,005,440.Although these simultaneous multilayer coating techniques can be used,best results are obtained when the paint layer is coated and driedseparately and then successive layers of the topcoat are coated anddried in two or more separate passes using an extrusion hopper as inU.S. Pat. No. 2,681,294 and drying each layer after it is coated.

The preferred transparent topcoat comprises a crosslinked polymer.Preferably it is formed by mixing a two-component crosslinkingcomposition such as a polymeric polyol solution and a diisocyanatesolution which react after mixing to form a crosslinked polyurethane. Incoating this composition the preferred procedure is to mix the reactivecomponents just before coating the mixture on the paint layer. Theprocedure is described in the copending patent application of Hayward etal, Ser. No. 189,090, filed May 2, 1988, now U.S. Pat. No. 4,832,991. Asthe application describes, the components are fed to a mixing zone andthe mixture is extruded in laminar flow through the narrow horizontalextrusion slot of a coating hopper within less than about 50 secondsafter being formed in the mixing zone.

The sheet material of this invention includes a thin flexible carrierfilm. The latter preferably comprises an essentially planar,self-supporting, stretchable, thermoplastic polymeric film. It can betransparent, translucent or opaque. If desired, it can be matched incolor to the color of the protective and decorative paint layer byincorporation of a colorant.

Suitable materials for the carrier film include stretchablethermoplastic polymeric films having heat softening and tensileelongation properties which adapt it to use in the thermoformingprocess. Preferred are those films known to be useful in thermoformingand/or vacuum-forming techniques, such as polyvinyl chloride, polyvinylacetate, ABS (acrylonitrile-butadiene-styrene) resins, polyethylene andpolypropylene. Useful materials include the polyacrylate blends withcopolyesters described in U.S. Pat. No. 4,246,381, and the copolyestersderived from aromatic polyesters and glycol polyesters described in U.S.Pat. No. 4,287,325. Blends of rubber-modified styrene-maleic anhydrideswith polycarbonates and/or polyesters are also useful, as are blends ofpoly(ether-esters) and polyesters. Particularly preferred supportmaterials exhibit a tensile elongation at break of at least about 40%when measured in accordance with ASTM D-638. A highly preferred supportmaterial is a blend of copolyesters based onpoly(1,4-cyclohexylenedimethylene terephthalate) and rubber-modifiedstyrene-maleic anhydride copolymers as described in U.S. Pat. No.4,582,876. Another preferred carrier film is the highly flexible filmmade from a blend of poly(etheresters and) polyesters as disclosed inthe copending patent application of Seymour Ser. No. 151,727 filed Feb.3, 1988, now U.S. Pat. No. 4,904,748. The carrier film can includefillers, UV absorbers, plasticizers, colorants, antioxidants, etc. knownto be useful in polymeric films.

The paint layer of the sheet material contains light-reflective flakesin addition to a binder and, optionally, a colorant and other addendasuch as surfactants, coalescing agents and the like. Thelight-reflective flakes can be those conventionally employed in paints,particularly those employed in automotive finish paints. These includemetallic flakes such as aluminum flake, copper flake, bronze flake,copper bronze flake, nickel flake, zinc flake, magnesium flake, silverflake, gold flake, and platinum flake and other flakes such as mica,glass, coated mica, coated glass and aluminum-coated polyester filmfragments. Mixtures of two or more types of such flakes can also beused.

Conventional paint colorants can be employed in combination with suchflakes, including inorganic pigments such as titanium, dioxide, ironoxide, chromium oxide, lead chromate, carbon black, silica, talc, chinaclay, metallic oxides, silicates, chromates, etc., and organic pigments,such as phthalocyanine blue, phthalocyanine green, carbazole violet,anthrapyrimidine yellow, flavanthrone yellow, isoindoline yellow,indanthrone blue, quinacridone violet, perylene reds, diazo red andothers.

The film-forming binder for the paint composition can comprise any ofthe film-forming resins conventionally used as binders in basecoatcompositions. Particularly useful are acrylic polymers, polyesters,including alkyds, and polyurethanes. Examples of such binders andmethods for the preparation thereof are described in U.S. Pat. Nos.4,681,811; 4,403,003 and 4,220,679.

Water-based basecoats in color plus-clear compositions are disclosed inU.S. Pat. No. 4,403,003, and the resinous compositions used in preparingthese basecoats can be used in the practice of this invention. Also,water-based polyurethanes such as those disclosed in U.S. Pat. Nos.4,147,679 and 4,719,132 can be used as the resinous binder in the paintlayer.

Preferred paints of those described above have been used on externalautomobile parts made from deformable polyurethanes. Such paints stretchand deform without cracking or delaminating.

The paint layer preferably has a thickness in the range of from about0.012 to 0.080 millimeters. A particularly preferred mean thickness isin the range of from about 0.020 to 0.060 millimeters.

The heat softening and tensile elongation properties of the paint layermust be compatible with those of the carrier film so as to permitsymmetrical elongation. By symmetrical elongation it is meant that thesheet material can undergo substantial elongation by the application ofstretching forces without splitting, crazing or delaminating of thepaint layer. Applicant's sheet material provides outstanding symmetricalelongation, which results in part from the thickness and thicknessuniformity of the layers. The ratio of the mean thickness of the paintlayer to the mean thickness of the support preferably is in the range of1.00 to 0.04 and more preferably in the range of 0.50 to 0.08. Sheetmaterials having thickness ratios of about 0.2 are especially preferredfor obtaining substantial symmetrical elongation without splitting,crazing or delaminating.

Transparent topcoat compositions for use with basecoats are well knownin the art. Especially useful are compositions comprising crosslinkablepolyols such as polyester polyols, polyurethane polyols and acrylicpolyols, admixed with polyisocyanate curing agents. In accordance withthis invention, the topcoat composition is extruded through a slot ontothe paint layer of the sheet material. This laminar flow method permitsthe coating of a thick crosslinkable topcoat in one or more passes andresults in improved smoothness, excellent gloss and distinctness ofimage, as compared with topcoats applied by spraying and othernon-laminar flow techniques. The topcoat is then dried to a tack-freestate.

The dried topcoat layer has a thickness of at least about 0.1millimeter, preferably of at least 0.125 millimeter. Highly preferred isa clear layer having a dried thickness of at least 0.15 millimeter.Applicant has achieved clearcoat thickness up to 0.25 millimeter usingthe coating techniques described above.

The carrier film, paint layer and topcoat layer have heat softening andtensile elongation properties which render the sheet material suitablefor use in the thermoforming process and which are mutually compatibleso as to permit symmetrical elongation, whereby the sheet material canundergo substantial elongation by the application of stretching forceswithout crazing or delamination of the basecoat and topcoat layers. Thecarrier film, paint layer and topcoat layer are of sufficiently uniformcharacter that the sheet material exhibits substantially the sameuniformity of appearance before and after the thermoforming process.

An adhesion-promoting tie-layer is coated on the carrier film before thebasecoat in preferred embodiments of the invention and provides improvedbonding strength and reduces the risk of delamination. Suitabletie-layers can be formed from compositions comprising an adhesionpromoting species and optionally a suitable solvent. Useful adhesionpromoting species include polymers derived from acrylonitrile,vinylidene chloride, and acrylic acid; polymers derived frommethylacrylate, vinylidene chloride and itaconic acid; cellulosenitrate, and a variety of commercially available adhesion promotingspecies, for example, those known under the trade designations FORMVAR7/95, FORMVAR 15/95, BUTVAR B-98 and BUTVAR B-72, sold by Monsanto,MOBAY M-50 sold by Mobay, VINAC B-15 sold by Air Products, ELVACITE soldby DuPont, and LEXAN sold by General Electric. Suitable solvents includemethylethyl ketone, methylene chloride, tetrahydrofuran, toluene, methylcellosolve, methanol, ethanol, propanol, butanol, mixtures thereof andthe like. The adhesion promoting layer preferably has a thickness notgreater than about 0.0025 millimeter. The thickness preferably issubstantially less than the thickness of the basecoat. For example, thebasecoat preferably has a thickness at least 8 times the thickness ofthe adhesion promoting layer.

It should be noted that the thermoforming process typically involvesstretching in all directions rather than just a longitudinal stretchingof the sheet material. Thus, the sheet material is extended in area.Prior to thermoforming, the sheet material can be said to be in arelaxed state in which it is substantially unstressed. By thethermoforming process, it is softened to a substantially plastic stateand plastically extended to an extended state. The sheet material ofthis invention is capable of extension to an extended area at least 50%greater than its relaxed area. Moreover, the sheet material of thisinvention is characterized by having a substantially uniform quality andappearance in both the relaxed and extended states.

As noted, the sheet material of the invention has a substantiallyuniform quality and appearance both in the relaxed and extended statesof the sheet material. This means that in the relaxed state it isessentially free of coating defects such as lines, dimples, bubbles,streaks, banding, repellencies, colorant agglomerations and the likewhen visually examined under roomlight, on a light box and in sunlight.Furthermore, this means that the sheet material provides a commerciallyacceptable finish when applied to exterior automobile panels. Moreover,a given relaxed size of sheet material can be stretched differentdegrees in different areas, or stretched in some areas and not in otherareas and the uniformity of appearance in all areas, includingdistinctness of image, gloss, optical density, and flop remainssubstantially the same.

The sheet material of this invention preferably exhibits an initialdistinctness of image (DOI) of at least 80 as measured by ASTM TESTE-430. Such measurements, for example, can be made on a HUNTERLAB MODELD47R-6 DORIGON GLOSSMETER. Preferred sheet materials of the inventionexhibit an initial DOI of at least 85, and more preferably of at least90 when measured by this technique.

The sheet material of this invention exhibits an initial 20° gloss of atleast 80 when measured in accordance with ASTM TEST D-523. Preferredsheet materials of this invention exhibit a 20° gloss of at least 85initially and more preferably of at least 90 when measured by thismethod. When stretched up to 50 percent more than the original area thegloss remains at least about 80.

The sheet material of this invention preferably exhibits an averagesurface roughness (Ra) of less than 0.4 micron when measured byconventional surface roughness measuring techniques known in the art.For example, Ra can be measured using a scanning type stylus instrumenthaving a skidless probe and a cutoff of about 0.030 in. One suchinstrument is the Micro-Topographer® sold by Federal ProductsCorporation. Particularly preferred sheet materials of this inventionexhibit an average surface roughness of less than 0.2 micron and morepreferably of less than 0.1 micron.

Laminar flow coating techniques are required in manufacturing the sheetmaterial of the invention. These include direct extrusion onto thesupport by use of an extrusion hopper functioning to apply the coatingcomposition by a bead coating or a stretch-flow coating mechanism,extrusion of the coating composition through a slot with subsequenttravel down the slide surface of a slide hopper or subsequent free fallin a curtain coating process and curtain coating processes in which thecurtain is generated by the use of an overflow weir. The critical aspectof the coating process is its ability to provide a defect-free coatingwith a very high degree of uniformity of layer thickness. In particular,the process must provide such a result even with a thick coating of thecrosslinking clearcoat composition.

The use of precision coating processes in the production of the sheetmaterial--such as the use of high precision extrusion hoppers--is animportant aspect of the present invention. In particular, the coatingoperation must be conducted with exacting control of all criticalparameters to ensure the high degree of thickness uniformity and thefreedom from coating defects that characterize the sheet material ofthis invention. Only by such control of both thickness uniformity andcoating defects, can sheet material be produced which is capable ofundergoing the rigors of the thermoforming process and yielding aproduct with the very high quality demanded of an automotive finish.

Laminar flow extrusion coating hoppers such as disclosed in the patentto Beguin, U.S. Pat. No. 2,681,294, are particularly effective devicesfor use in the process of this invention. Such devices are well-adaptedfor use with shear-thinning compositions typical of the paintcompositions hereinbefore described. In such hoppers, transversepressure gradients are minimized and almost all pressure drop across theslot is in the direction of coating. While applicant does not wish to bebound by any theoretical explanation of the manner in which hisinvention functions, it is believed that such features contribute to theexcellent results achieved with an extrusion hopper, especially in thecoating of paint compositions containing light reflective flakes and inthe coating of crosslinking clearcoat compositions.

EXAMPLES

The invention is further illustrated by the following examples:

EXAMPLE 1

A carrier film was prepared from a blend described in U.S. Pat. No.4,582,876 as follows:

A mixture of 55:45 parts by weight of polyester (1) and Dylark® SytreneCopolymer 600 was compounded by extrusion. Polyester (1) was derivedfrom terephthalic acid, 19 mole % ethylene glycol and 81 mole %1,4-cyclohexanedimethanol. Dylark® Styrene Copolymer 600 is a rubbermodified styrene-maleic anhydride copolymer available from ARCO ChemicalCompany, a division of Atlantic Richfield Company.

The blend was heated to 260°-290° C. and extruded through a die into anip comprising two temperature-controlled chrome plated stainless steelrollers. The extruded web was then cooled on a chill roller. Thethermoplastic film had a mean thickness of about 0.20 mm and a maximumthickness deviation of less than 0.02 mm.

The carrier film prepared as described above was extrusion coated with athin tie-layer composition (diluted to 5% solids before coating). Beforebeing diluted the composition comprised 75% water, 10% acrylic resin,10% urethane resin, 1% methylpyrrolidone, 1% diethyleneglycol monobutylether, less than 1% ethylene glycol monohexyl ether, less than 1% N,N-dimethyl ethanolamine and about 0.05% FC 170 surfacant (sold by 3MCompany). The diluted composition was coated through a 0.13 millimeterslot and dried at 40°-90° C. All percentages are by weight. The drycoverage was 0.54 g/m², the dry thickness being 0.0005-0.001 mm.

The metallic paint composition described below was metered from anitrogen gas pressurized vessel through a coating hopper extrusion slothaving a width of 0.25 millimeter onto the carrier film moving at aspeed of 8 m/min. The coating roll was cooled with recirculating waterto reduce the propensity of the coating to streak and to minimizeprecipitate formation on the hopper lip. The coating method andapparatus were substantially as described in U.S. Pat. No. 2,681,294 andincluded means for maintaining a pressure differential across oppositesurfaces of the coating ribbon. The coating was dried at 27°-80° C. (drycoverage 43 g/m² and 0.6 mm thickness) in a plural-stage, continuousflat bed drying apparatus supplied with low velocity, warm air streams.

    ______________________________________                                        Metallic Paint Composition                                                    Ingredient            Approx. % Weight                                        ______________________________________                                        Deionized water       50                                                      Urethane resin        25                                                      Aluminum paste        5                                                       Ethylene Glycol Monohexyl Ether                                                                     5                                                       N-Methylpyrrolidone   5                                                       Diethylene Glycol Monobutyl Ether                                                                   1                                                       N,N-Dimethyl Ethanolamine                                                                           1                                                       Xylene                1                                                       Aliphatic Solvent Naphtha                                                                           1                                                       Isopropyl Alcohol     <1                                                      ______________________________________                                    

The dried, paint-coated web was wound on a take-up roll and again drawnthrough a coating station to form over the paint layer a uniform layerof a clear topcoat of the composition described below.

    ______________________________________                                        Clear Topcoat Composition                                                                        Approx. % Weight                                           ______________________________________                                        Component A                                                                   Urethane Resin (polyol)                                                                            60                                                       Toluene              40                                                       Benzotriazole         1                                                       (diluted to 51% solids with acetone)                                          Component B*                                                                  Polyfunctional       100                                                      aliphatic isocyanurate                                                        resin based on                                                                1,6-hexamethylene                                                             diisocyante                                                                   ______________________________________                                         *Available as Desmodur N3300 from Mobay Corporation Coatings Division    

Components A and B were mixed by means of an in-line mixer beforereaching the coating hopper as described in the Hayward et al. patentapplication Ser. No. 189,090 now U.S. Pat. No. 4,832,991, cited above.The composition flowed from the mixer directly to an extrusion coatinghopper of the type disclosed in U.S. Pat. No. 2,681,294 and wasextrusion coated, in a single pass, through the narrow extrusion slot ofthe hopper. The web having on its surface the wet topcoat layer was thenpassed directly to a drying chamber where the topcoat layer was driedand cured by exposure to low velocity streams of warm, moderately humidair in a series of stages of successively increasing temperatures, thedrying and curing procedure being substantially as disclosed in theFronheiser et al. application Ser. No. 166,083 now U.S. Pat. No.4,872,270 cited above. The dried clear topcoat layer applied in thissingle pass had a thickness of 0.03 mm. The so prepared sheet materialwas designated sheet material 1. A pressure sensitive adhesive layer wasapplied to the backside of the carrier film as described in the patentapplication, Ser. No. 116,426 now abandoned.

Another sheet material 2 was prepared in the same manner except that theclear topcoat was applied in two passes. The total dry thickness of thetopcoat of sheet material 2 was 0.06 mm.

Thereafter a sheet material of the invention, sheet material 3, wasprepared in the same manner except that the clear topcoat was applied infour passes. The total dry thickness of the topcoat of sheet material 3was 0.12 mm.

A sample of each sheet material was heated by infra-red lamps to atemperature of about 135° C. and then drawn by vacuum thermoforming intocontact with a 7.5×30 cm inclined metal panel and adhesively bondedthereto. As they were drawn down onto the inclined panels, the samplesstretched by an amount proportional to the distance along the panel, thearea at the top of the panel (Top) having little or no stretch, and anarea half-way down the panel (Center) having a stretch of about 70percent.

Gloss and DOI measurements made at the top and center areas on eachpanel indicate the effect of stretching on the surface characteristicsof the sheet material.

Gloss was measured by the ASTM D-523 method mixing a Hunter 20-DegreeASTM Glossmeter, and Distinctness of Image (DOI) was measured by theASTM Test E-430 method using a Hunterlab Model D47R-6 DorigonGlossmeter.

The results are shown in Table 1.

                  TABLE 1                                                         ______________________________________                                        Topcoat      Gloss         DOI                                                Sheet  Thickness              %               %                               Material                                                                             (mm)      Top    Center                                                                              Loss Top  Center                                                                              Loss                            ______________________________________                                        1      0.03      70     14    (80) 16   3     (81)                            2      0.06      88     42    (52) 29   7     (76)                            3      0.12      94     80    (15) 90   41    (54)                            ______________________________________                                    

The data show that an increase in the thickness of the clear topcoatprovides

a) improvement in the initial gloss and DOI in unstretched areas of thethermoformed sheet material (top of the panel), and

b) reduction in the loss of gloss and DOI at the panel center afterthermoforming and stretching of the sheet material. Thus only 15% lossof gloss occurred with the sheet material of the invention as comparedwith 52 and 80% loss with the thinner topcoat materials. Likewise, theloss of DOI with the sheet material of the invention was much less,namely 54% as compared with 81 and 76%.

Each of the sheet material samples was thermoformed and bonded to aninclined metal test panel as in Example 1.

EXAMPLE 2

Four sheet material samples were prepared and evaluated as in Example 1.The paint layer of each of the samples was formed from the metallicflake composition of Example 1. The dry thickness of the clear topcoatswere approximately 0.07, 0.1, 0.2 and 0.25 mm, respectively.

Non-Flake Paint Example

Four additional sheet material samples were prepared and evaluated asdescribed in Example 1. The paint layer for each sample was formed froma non-metallic white paint of the composition shown below. The cleartopcoats had the same thicknesses as in Example 2.

Non-Flake Paint Composition

    ______________________________________                                        Ingredient            Approx. % Weight                                        ______________________________________                                        Titanium Dioxide      25                                                      Ethylene Glycol Monohexyl Ether                                                                     5                                                       Diethylene Glycol Monobutyl Ether                                                                   1                                                       Deionized Water       45                                                      N,N-Dimethyl Ethanolamine                                                                           1                                                       N-Methylpyrrolidone   5                                                       Urethane Resin        20                                                      ______________________________________                                    

The retained gloss data, measured at the panel center for each of thestretched sheet materials of Example 2 and of the Non-Flake PaintExample are graphically illustrated in FIG. 4.

FIG. 4 shows that:

(a) gloss retention improves with increasing topcoat thickness inthermoformed sheet materials having a paint layer which contains lightreflective flakes; and

(b) the topcoat thickness has no apparent effect on gloss retention inthermoformed sheet materials having a paint layer which contains noflakes.

The manufacture of thermoformable films coated with flake-containingpaints and having thick-crosslinked clearcoats is not believed to besuggested by the prior art. Thus it is not believed predictable that afilm having a flake-containing paint layer which normally decreases ingloss when stretched, could be protected against loss of gloss or DOI byincreasing to greater than 0.1 mm the thickness of the clearcoat whichis coated and dried over the paint layer. It is entirely unexpected thatsuch a thick crosslinked clearcoat would provide this benefit. Even moreimportantly, it has not heretofore been possible to obtain a method formanufacturing successfully a sheet material having such a thickcrosslinked clearcoat and having the other characteristics of theapplicant's sheet material, such as freedom from coating defects andextreme uniformity in thickness, appearance and quality. It is believedthat any attempts to form such thick crosslinked clearcoats on apaint-coated thermoformable film by conventional automobile spraycoating techniques or by other non-laminar flow methods will result indefective products.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention.

What is claimed is:
 1. A protective and decorative sheet material forcovering substrates comprising:a thin flexible carrier film; aprotective and decorative paint layer adhered to one surface of saidcarrier film; said paint layer containing generally flat lightreflective flakes; a transparent topcoat layer overlying said paintlayer, said topcoat layer having a thickness of at least about 0.1millimeter; said sheet material having a substantially unstressedrelaxed state and a relaxed area; said sheet material being heatsoftenable to a substantially plastic state in which it is plasticallyextendable and formable over irregular surfaces to an extended statehaving an extended area at least 50% greater than said relaxed area; andsaid paint layer being adhered to said carrier film and said topcoatlayer being adhered to said paint layer and both layers having asubstantially uniform quality and appearance in both said relaxed andextended states of said sheet material.
 2. A sheet material according toclaim 1 wherein at least 75% of the flakes have an orientation within 12degrees of parallelism with the outer surface of said paint layer. 3.The sheet material of claim 1 including an adhesion promoting layerbetween said carrier film and said paint layer.
 4. The sheet material ofclaim 1 wherein said topcoat layer is a substantially clear layer of acrosslinked polyurethane.
 5. The sheet material of claim 1 including apressure-sensitive adhesive layer on the opposite side of said carrierfilm from said paint layer.
 6. The sheet material of claim 1 whereinsaid carrier film comprises a thin, essentially planar stretchablethermoplastic polymeric film of substantially uniform thickness.
 7. Thesheet material of claim 1 wherein the flakes are metallic flakes.
 8. Thesheet material of claim 1 wherein said light reflective flakes arealuminum flakes.
 9. A flexible and stretchable sheet material adaptedfor use in a thermoforming process in which it is stretched to conformto a three-dimensional substrate and bonded thereto so as to form asmooth and wrinkle-free protective and decorative coating thereon, saidsheet material comprising:(1) a thin, essentially planar, stretchable,thermoplastic polymeric carrier film of substantially uniform thickness;and (2) a thin protective and decorative paint layer of substantiallyuniform thickness on one surface of said thermoplastic polymeric carrierfilm, said paint layer comprising light reflective metallic flakesincorporated in a film-forming binder; (3) a substantially clear topcoatlayer of at least 0.1 millimeter uniform thickness adhered to said paintlayer; said thermoplastic polymeric carrier film having heat-softeningand tensile elongation properties which adapt it to use in saidthermoforming process; said paint layer and said topcoat layer havingheat-softening and tensile elongation properties that are compatiblewith those of said thermoplastic polymeric carrier film so as to permitsymmetrical elongation, whereby said sheet material can undergosubstantial elongation by the application of stretching forces withoutcrazing or delamination of said paint layer or said topcoat layer. 10.The sheet material of claim 1 wherein said carrier film comprises ablend of copolyesters based on poly(1,4-cyclohexylonedimethyleneterephthalate) and styrene maleic anhydride copolymers.